1. Field of Invention
This invention relates to degassing well water by displacing offensive gases by treatment with a stream of compressed air. The basic problem has existed for thousands of years. In recent years there has been recognition that subterranean water sources sometimes contained dissolved radon, prompting analytical procedures for measuring the radon content of water. The molar concentration of dangerous levels of radon are significantly smaller than the tolerable, innocuous molar concentrations of offensive gases such as sulfur dioxide, so that the problem of removing radon from water can be said to begin with concentrations smaller than are acceptable end results for other offensive gases. Some health authorities have indicated that other than inhaling smoke, radon is the second most abundant cause of lung cancer, which kills millions globally every decade. Because of the need for providing assurances that the radon concentration is so remarkably small, de-radonizing water is quite distinguishable from conventional degassing of water.
2. Prior Art
Therapeutic spas have been developed in locations where the natural water from springs or well contained carbon dioxide and/or other gaseous components. Hydrogen sulfide, sulfur dioxide, oxides of nitrogen, methyl mercaptan, and/or other offensive gases have sometimes been detected in spring water, well water, and/or other natural sources for a water supply. Measurements of the radon content of natural water have been made for decades, particularly by mining geologists searching for deposits containing commercial concentrations of uranium. For several years, some householders seeking an analysis of their domestic well water have had the option of paying extra for a report on the radon content. Because helium is extremely insoluble in water, and because radon is also an inert gas, one might expect radon to be extremely insoluble. Water solubilities of gases are approximately inversely proportional to Henry's constant, so that a smaller Henry's constant indicates greater solubility and a larger Henry's constant indicates less solubility of the gas in water. Such constants are usually expressed as a number times 10 to the minus 7. At page 1398-9 of the 30th Edition of the Handbook of Chemistry and Physics, the significant figures for such Henry's constants at 10 degrees Centigrade were: helium, 10.5; radon 0.286; carbon dioxide, 0.0788; nitrous oxide 0.108; and ethylene 0.552.
Removing radon from the atmosphere of a home has become a retrofitting skill which has attractive cost-benefit ratios under appropriate conditions, notwithstanding the fact that some homes are so located that the normal radon concentration may be either too small or too great to justify the costly renovations required for modifying the exposure to radon.
Well water can contain dissolved radon. Any mammal ingesting water containing radon is risking that such radon may initiate, not merely lung cancer, but any of dozens of other kinds of cancer and illness. Public health authorities recognize that the cost-effectiveness of measuring the radon content of every domestic well is questionable. However, those wells employed for supplying water to hundreds of homes can be monitored for banning the further use of wells contaminated with dangerous concentrations of radon.
New standards have recently been announced for the radon content of public water systems. Hence, consumers are scheduled to be protected from the cancer hazards attributable to radon in public water supplies. There has been widespread recognition that removing radon was significantly more difficult than removing conventional objectionable gases. The effort to remove an objectionable gas from a liquid has sometimes been called "degassing" notwithstanding the fact that the process involved the substituting air for the objectionable gas dissolved in the liquid.
Although abandonment of a well having troublesome amounts of radon is among the contemplated responses to the discovery of radon concentrations above the established standards, various procedures are available for decreasing the radon concentration. Heretofore there have been proposals for the use of vacuum and/or reduced pressure for degassing water supplies, and relatively bulky equipment has been proposed for such processing. Other systems have modified the pressurized water system to depressurize the water for spraying through a flowing air stream so that the objectionable gas has been withdrawn as the water was fully aerated at ambient pressure, and the thus aerated water has been then repressurized for use in the water supply system.
Although some aspects of small water supply systems for a household and large water supply systems for public distribution have been similar, the technologies for removing objectionable gases from the two types of systems have developed as quite distinct technologies. One standard method for degassing a municipal water supply has involved the spraying of water downwardly in a tower in which the upflowing air stream carried away the objectionable gases. After such degassing, the water required repressurization. The capital and operating costs for such standard degassing system prompted descriptions of dozens of alternative proposals, most of which proved sufficiently unsatisfactory that the spraying into a counter-flowing air stream remained a standard procedure. Some of these above-ground treatments have required depressurizing the water, and then bubbling compressed air through such depressurized water, venting the gaseous mixture of radon and air stream resulting from such treatment, and then repressurizing the degassed water. If the air which is compressed contains bacteria, such bubbling of compressed air can contaminate the water. If the bubbling of the compressed air through the water is in a building, then some of the radon removed from the water might leak into the building instead of being adequately vented to the outdoors.
Water derived from a subterranean source has sometimes been de-radonized by treatment with activated charcoal. However, any activated charcoal containing significant amounts of radon and/or its decomposition products is a hazordous waste which requires costly disposal.